// INFO: This shader is a port of https://www.shadertoy.com/view/3sySRK

// INFO: Change these variables to create some variation in the animation
#define BLACK_BLEND_THRESHOLD .4 // This is controls the dim of the screen
#define COLOR_SPEED 0.1          // This controls the speed at which the colors change
#define MOVEMENT_SPEED 0.1       // This controls the speed at which the balls move

float opSmoothUnion(float d1, float d2, float k)
{
    float h = clamp(0.5 + 0.5 * (d2 - d1) / k, 0.0, 1.0);
    return mix(d2, d1, h) - k * h * (1.0 - h);
}

float sdSphere(vec3 p, float s)
{
    return length(p) - s;
}

float map(vec3 p)
{
    float d = 2.0;
    for (int i = 0; i < 16; i++) {
        float fi = float(i);
        float time = iTime * (fract(fi * 412.531 + 0.513) - 0.5) * 2.0;
        d = opSmoothUnion(
                sdSphere(p + sin(time * MOVEMENT_SPEED + fi * vec3(52.5126, 64.62744, 632.25)) * vec3(2.0, 2.0, 0.8), mix(0.5, 1.0, fract(fi * 412.531 + 0.5124))),
                d,
                0.4
            );
    }
    return d;
}

vec3 calcNormal(in vec3 p)
{
    const float h = 1e-5; // or some other value
    const vec2 k = vec2(1, -1);
    return normalize(k.xyy * map(p + k.xyy * h) +
            k.yyx * map(p + k.yyx * h) +
            k.yxy * map(p + k.yxy * h) +
            k.xxx * map(p + k.xxx * h));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec2 uv = fragCoord / iResolution.xy;

    vec3 rayOri = vec3((uv - 0.5) * vec2(iResolution.x / iResolution.y, 1.0) * 6.0, 3.0);
    vec3 rayDir = vec3(0.0, 0.0, -1.0);

    float depth = 0.0;
    vec3 p;

    for (int i = 0; i < 64; i++) {
        p = rayOri + rayDir * depth;
        float dist = map(p);
        depth += dist;
        if (dist < 1e-6) {
            break;
        }
    }

    depth = min(6.0, depth);
    vec3 n = calcNormal(p);
    float b = max(0.0, dot(n, vec3(0.577)));
    vec3 col = (0.5 + 0.5 * cos((b + iTime * COLOR_SPEED * 3.0) + uv.xyx * 2.0 + vec3(0, 2, 4))) * (0.85 + b * 0.35);
    col *= exp(-depth * 0.15);

    vec2 termUV = fragCoord.xy / iResolution.xy;
    vec4 terminalColor = texture(iChannel0, termUV);

    float alpha = step(length(terminalColor.rgb), BLACK_BLEND_THRESHOLD);
    vec3 blendedColor = mix(terminalColor.rgb * 1.0, col.rgb * 0.3, alpha);

    fragColor = vec4(blendedColor, terminalColor.a);
}